Optical time-domain reflectometer interoperable trunk switch

ABSTRACT

An optical trunk switch is configured to support an OTDR. The system includes a transmit switch having two inputs and outputs, the first input is configured to connect to a signal input, the second input is configured to receive a OTDR signal, the first output is configured to connect to one of a primary fiber and a standby fiber, and the second output is configured to connect to the other fiber. The system further includes a receive switch having two inputs and outputs, the first input is configured to connect to one of the primary fiber and the standby fiber, the second input is configured to connect to the other fiber, the first output is configured to connect to a signal output, and the second output is configured to connect to a OTDR signal; and one or more OTDR ports.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present disclosure is a divisional of U.S. patent application Ser.No. 16/270,636, filed Feb. 8, 2019, and entitled “Optical time-domainreflectometer interoperable trunk switch,” which is a divisional of U.S.patent application Ser. No. 15/712,214, filed Sep. 22, 2017 (now U.S.Pat. No. 10,250,324, issued Apr. 2, 2019), and entitled “Opticaltime-domain reflectometer interoperable trunk switch,” the contents ofeach are incorporated by reference herein.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to optical networking systemsand methods. More particularly, the present disclosure relates to anOptical Time-Domain Reflectometer (OTDR) Interoperable Trunk Switch.

BACKGROUND OF THE DISCLOSURE

Optical trunk switches (also referred to as Optical Protection Switches(OPSs), optical switches, etc.), are all-optical devices that enable asingle client (0:1) to support line-side protection (1+1, 1:1, opticalring protection, etc.). Specifically, an optical trunk switch can take asingle optical channel (TX/RX) and provide it on two redundant fiberpaths. These devices are designed to automatically detect trafficinterruptions and quickly reroute/switch traffic from a primary fiberpath to a standby fiber path. Optical trunk switches can be deployed invarious scenarios, such as metro networks, Data Center interconnects,etc. Advantageously, optical switches are used to reduce clientinterfaces since a vast majority of faults are on the line side such asin the optical network affecting one of the lines. That is, fiber cutsor other failures in the optical network are more common than equipmentfailures, thus optical trunk switches provide a cost-effective approachto offer redundancy.

Also, Optical Time-Domain Reflectometer (OTDR) is a feature that isincreasingly becoming commonplace in network deployments, such asintegrated OTDR systems in an optical line system, i.e., integrated intomodems, amplifiers, multiplexers, Reconfigurable Optical Add-DropMultiplexers (ROADMs), etc. An OTDR provides detailed distancereferenced characterization of the physical fiber plant. The OTDRgenerally operates by sending optical test signals into the fiber anddetecting, at the same end, the scattered (Rayleigh backscatter) orreflected back light from points along the fiber. This information helpsoperators monitor and detect fiber span related issues, e.g., bad orpoor slices, high attenuation, physical defects, etc.

At present, there is an incompatibility between optical trunk switchesand OTDR based on the structure of conventional optical trunk switches.Specifically, optical trunk switches typically broadcast a transmitsignal on both the primary and standby fiber and switch a receivedsignal from only one of the primary and standby fiber. Thus, there is noconventional approach to use OTDR with an optical trunk switch tomonitor both the primary and standby fibers while in-service. That is,the conventional optical trunk switch would send an OTDR test signalover both the primary and standby fibers in the transmit direction andonly receive the OTDR test signal in the receive direction based onwhich fiber is currently active.

BRIEF SUMMARY OF THE DISCLOSURE

In an embodiment, an optical trunk switch supporting an OpticalTime-Domain Reflectometer (OTDR) includes a transmit switch configuredto provide an input signal to one or more of a primary fiber path and astandby fiber path; a receive switch configured to provide an outputsignal from one of the primary fiber path and the standby fiber path;and an OTDR connection configured to provide one or more OTDR signals tomonitor an inactive path of the primary fiber path and the standbyfiber. The transmit switch and the receive switch each can include a 2×2switch. The OTDR connection can be connected separately to each of thetransmit switch and the receive switch to provide a co-propagating OTDRsignal on the inactive path in a transmit direction and acounter-propagating OTDR signal on the inactive path in a receivedirection. The OTDR connection can include an OTDR port connected to anexternal module which supports the one or more OTDR signals to monitorthe inactive path. The OTDR connection can include an integrated OTDRsystem in the optical trunk switch. The one or more OTDR signals caninclude a co-propagating OTDR signal to monitor a transmit direction ofthe inactive path and a counter-propagating OTDR signal to monitor areceive direction of the inactive path. The optical trunk switch caninclude a splitter connected to the OTDR connection and configured tosplit the co-propagating OTDR signal and the counter-propagating OTDRsignal to a respective one of the transmit switch and the receiveswitch. The transmit switch can include a 1×2 splitter and the receiveswitch can include a 2×2 switch, and wherein the OTDR connection isconnected to the 2×2 switch to provide a counter-propagating OTDR signalto monitor a receive direction of the inactive path. The OTDR connectioncan receive an OTDR signal and connect to a 1×2 switch which isconfigured to selectively provide the OTDR signal as one of aco-propagating OTDR signal in a transmit direction on the inactive pathand a counter-propagating OTDR signal in a receive direction on theinactive path.

In another embodiment, an optical trunk switch supporting an OpticalTime-Domain Reflectometer (OTDR) includes a transmit 2×2 switchconfigured to provide an input signal to an active path and to provide aco-propagating OTDR signal to an inactive path; a receive 2×2 switchconfigured to provide an output signal from the active path and toprovide a counter-propagating OTDR signal to the inactive path; and anOTDR connection for the co-propagating OTDR signal and thecounter-propagating OTDR signal. The OTDR connection can be connectedseparately to each of the transmit switch and the receive switch toprovide the co-propagating OTDR signal on the inactive path in atransmit direction and the counter-propagating OTDR signal on theinactive path in a receive direction. The OTDR connection can include anOTDR port connected to an external module which supports theco-propagating OTDR signal and the counter-propagating OTDR signal tomonitor the inactive path. The OTDR connection can include an integratedOTDR system in the optical trunk switch. The optical trunk switch caninclude a splitter connected to the OTDR connection and configured tosplit the co-propagating OTDR signal and the counter-propagating OTDRsignal to a respective one of the transmit 2×2 switch and the receive2×2 switch. The OTDR connection can receive an OTDR signal and connectto a 1×2 switch which is configured to selectively provide the OTDRsignal as one of the co-propagating OTDR signal in a transmit directionon the inactive path and the counter-propagating OTDR signal in areceive direction on the inactive path.

In a further exemplary embodiment, a method for providing an opticaltrunk switch supporting an Optical Time-Domain Reflectometer (OTDR)includes providing a transmit switch configured to provide an inputsignal to one or more of a primary fiber path and a standby fiber path;providing a receive switch configured to provide an output signal fromone of the primary fiber path and the standby fiber path; and providingan OTDR connection configured to provide one or more OTDR signals tomonitor an inactive path of the primary fiber path and the standbyfiber. The transmit switch and the receive switch each can include a 2×2switch. The OTDR connection can include an OTDR port connected to anexternal module which supports the one or more OTDR signals to monitorthe inactive path. The OTDR connection can include an integrated OTDRsystem in the optical trunk switch. The one or more OTDR signals caninclude a co-propagating OTDR signal to monitor a transmit direction ofthe inactive path and a counter-propagating OTDR signal to monitor areceive direction of the inactive path.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is illustrated and described herein withreference to the various drawings, in which like reference numbers areused to denote like system components/method steps, as appropriate, andin which:

FIG. 1 is a block diagram of a conventional optical trunk switch using asplitter in the transmit direction and a 1×2 switch in the receivedirection;

FIG. 2 is a block diagram of a conventional optical trunk switch using1×2 switches in both the transmit direction and the receive direction;

FIG. 3 is a block diagram of a convention optical trunk switch using a2×2 switch in the transmit direction and a 1×2 switch in the receivedirection;

FIG. 4 is a block diagram of an OTDR interoperable trunk switch using a2×2 switch in both the transmit direction and the receive direction andwith an OTDR port enabling OTDR signals over both the primary fiber pathand the and standby fiber path regardless of which is currently set asthe active fiber path;

FIG. 5 is a block diagram of the OTDR interoperable trunk switch withthe 2×2 switches switched from the configuration of FIG. 4;

FIG. 6 is a block diagram of an OTDR interoperable trunk switch with anOTDR port which provides separate inputs for the OTDR signals;

FIG. 7 is a block diagram of an OTDR interoperable trunk switch with anOTDR port supporting a single wavelength counter-propagating OTDR signalfor unidirectional OTDR monitoring;

FIG. 8 is a block diagram of an OTDR interoperable trunk switch with anOTDR port supporting a single wavelength counter-propagating OTDR signalalong with a 1×2 switch for bidirectional OTDR monitoring;

FIG. 9 is a block diagram of an OTDR interoperable trunk switch with anintegrated OTDR system;

FIGS. 10-14 are network diagrams of OTDR interoperable trunk switchesinterconnected by the primary fiber path and the standby fiber pathillustrating a sequence of events based on a fiber cut; and

FIG. 15 is a block diagram of an OTDR module interconnected to the OTDRinteroperable trunk switch.

DETAILED DESCRIPTION OF THE DISCLOSURE

In various embodiments, the present disclosure relates to an OpticalTime-Domain Reflectometer (OTDR) Interoperable Trunk Switch. The OTDRinteroperable trunk switch supports unidirectional or bidirectional OTDRmonitoring of both the primary and standby fiber paths in-service.Generally, the OTDR interoperable trunk switch includes one or moreadditional optical ports to support the inclusion of OTDR test signalsfor monitoring an inactive fiber path. Advantageously, the OTDRinteroperable trunk switch enables operators to monitor both active andinactive fiber paths extending OTDR support to optical trunk switches.Various embodiments are described which support dual or singlewavelength (WL) OTDR signals as well as unidirectional and bidirectionalmonitoring. The unidirectional monitoring supports one fiber direction(e.g., counter-propagating in the receive direction). The bidirectionalmonitoring supports both fiber directions (i.e., co-propagating in thetransmit direction and counter-propagating in the receive direction).The dual wavelength OTDR signals enable the additional optical port toreceive both co-propagating and counter-propagating signals on the samefiber with an integrated splitter configured to split the separatewavelengths.

Conventional Optical Trunk Switch

FIG. 1 is a block diagram of a conventional optical trunk switch 10Ausing a splitter 12 in the transmit direction and a 1×2 switch 14 in thereceive direction. In operation, the splitter 12 is configured toreceive an input signal 16 in the transmit direction and split the sameinput signal to both a primary fiber path 18 and a standby fiber path20. The 1×2 switch 14 is configured to receive an output signal 22 fromboth the primary fiber path 18 and the standby fiber path 20 and toprovide only the output signal 22 from an active fiber based on the 1×2switch 14 setting. For example, the optical trunk switch 10A can includedetectors 24 which are used to set the 1×2 switch 14. The detectors 24can also provide monitoring of the signals from the splitter 12. Theoutput signal 22 can include the input signal 16 from an adjacentoptical trunk switch 10A (i.e., remote node) which has been provided toboth the fiber paths 18, 20.

OTDR signals are incompatible with the optical trunk switch 10A. Aco-propagating OTDR signal 26 travels both paths based on the splitter12, and thus it is impossible to resolve to which path (i.e., whichfiber path 18, 20) a reflection event belongs. A counter-propagatingOTDR signal 28 would only monitor the active path based on the settingof the 1×2 switch 14.

FIG. 2 is a block diagram of a conventional optical trunk switch 10Busing 1×2 switches 14 in both the transmit direction and the receivedirection. The optical trunk switch 10B operates in a similar manner asthe optical trunk switch 10A in the receive direction. However, thesplitter 12 is replaced with a 1×2 switch 14 which directs the inputsignal 16 based on the setting of the 1×2 switch 14, i.e., the transmitdirection only sends one copy of the input signal 16 on the active fiberof the fiber path 18, 20. Here, the OTDR signals 26, 28 can monitor apath since only one copy is sent in the transmit direction. However, theoptical trunk switch 10B can only support OTDR monitoring in the activepath.

FIG. 3 is a block diagram of a conventional optical trunk switch 10Cusing a 2×2 switch 30 in the transmit direction and a 1×2 switch 14 inthe receive direction. The optical trunk switch 10C operates in asimilar manner as the optical trunk switches 10A, 10B in the receivedirection. However, the transmit direction includes the 2×2 switch 30which is configured to provide the input signal 16 to the active fiberbased on the settings of the 2×2 switch 30. Additionally, the 2×2 switch30 has a second input 32 which is sent to the inactive fiber based onthe settings of the 2×2 switch 30. For example, the second input 32 canbe connected to a pilot tone which simply provides a connectivityverification at an adjacent optical trunk switch 10C. The pilot tone cansimply be a signal at a specified wavelength or Amplified StimulatedEmission (ASE). The optical trunk switch 10C has the same issues relatedto OTDR as the optical trunk switch 10B, here again, the co-propagatingand counter-propagating OTDR signals 26, 28 would only monitor theactive path.

OTDR Interoperable Trunk Switch—Dual Wavelength (WL) and Bidirectional

FIG. 4 is a block diagram of an OTDR interoperable trunk switch 100using 2×2 switches 30A, 30B in both the transmit direction and thereceive direction and with an OTDR port 102 enabling OTDR signals overboth the primary fiber path 18 and the standby fiber path 20 regardlessof which is currently set as the active fiber path. Specifically, theOTDR interoperable trunk switch 100 uses dual wavelengths for the OTDRsignals 26, 28, 26A, 28A and supports bidirectional OTDR monitoring ofboth fiber paths 18, 20.

The OTDR interoperable trunk switch 100 can include a housing 104 withthree client-side ports 102, 106, 108 and four line-side ports 110, 112,114, 116. The client-side port 106 is configured to receive the inputsignal 16 along with the co-propagating OTDR signal 26 and connects toan input port of the 2×2 optical switch 30A. The co-propagating OTDRsignal 26 is configured to provide OTDR monitoring in the transmitdirection on the active fiber (pair). As described herein, the physicalfibers include the primary fiber path 18 and the standby fiber path 20.These fiber paths 18, 20 can further be categorized as active andinactive, and either can be active or inactive based on the settings ofthe 2×2 optical switches 30A, 30B.

The client-side port 108 is configured to receive the output signal 22from the 2×2 optical switch 30B in the receive direction and to providethe counter-propagating OTDR signal 28 to the optical switch 30B. Thecounter-propagating OTDR signal 28 is configured to provide OTDRmonitoring in the receive direction on the active fiber (pair). Thus,from an OTDR perspective, the OTDR interoperable trunk switch 100operates in a similar manner as the OTDR interoperable trunk switches10B, 10C in terms of monitoring the active fiber (pair).

Additionally, the OTDR interoperable trunk switch 100 includes the OTDRport 102 to receive OTDR signals 26A, 28A for monitoring the inactivefiber path which is the standby fiber path 20. In this example, the OTDRport 102 is shown as a single port carrying both the OTDR signals 26A,28A at different wavelengths. The OTDR interoperable trunk switch 100can include for example a red/blue splitter 120 which splits the OTDRsignals 26A, 28A between the transmit direction and the receivedirection. The red/blue splitter 120 is configured to send the OTDRsignal 26A to the 2×2 optical switch 30A and the OTDR signal 28A to the2×2 optical switch 30B. The 2×2 optical switches 30A, 30B enable theinactive fiber path which is the standby fiber path 20 to receive theOTDR signals 26A, 28A thus enabling OTDR monitoring of the inactivefiber path which is the standby fiber path 20. Note, the OTDR port 102can be two separate ports each connected to a respective 2×2 opticalswitch 30A, 30B without requiring the red/blue splitter 120.

The 2×2 switches 30A, 30B are a cross-bar switch which receives twoinputs and can provide each of the two inputs to either output based onthe current settings. In FIG. 4, the 2×2 switches 30A, 30B are shownwith the top input connected to the top output and the bottom inputconnected to the bottom output. Thus, the client-side port 106 isconnected to the line-side port 110 which connects to the primary fiberpath 18 in the transmit direction. The client-side port 108 is connectedto the line-side port 116 which connects to the primary fiber path 18 inthe receive direction. The standby fiber path 20 is inactive in thisexample, and the line-side port 112 is connected to the OTDR port 102receiving the co-propagating OTDR signal 26A. The line-side port 114 isconnected to the OTDR port 102 receiving the counter-propagating OTDRsignal 28A. Thus, the OTDR signals 26A, 28A can monitor the standbyfiber path 20 which is inactive. In a switch scenario where the standbyfiber path 20 becomes active, the 2×2 switches 30A, 30B would switch thetop ports to the bottom ports.

The use of 2×2 cross-bar switches at both the near and far end allowsboth co-propagating and/or counter-propagating OTDR signals 26, 28, 26A,28A to be injected into the active and standby fiber plantsimultaneously. This capability allows the OTDR signals 26, 28, 26A, 28Ato monitor the standby fiber path and also to validate a repair beforedeclaring a damaged fiber path usable again.

FIG. 5 is a block diagram of the OTDR interoperable trunk switch 100with the 2×2 switches 30A, 30B switched from the configuration of FIG.4. Again, in FIG. 4, the OTDR signals 26, 28 provide OTDR monitoring ofthe active fiber path which is the primary fiber path 18. The OTDRsignals 26A, 28A from the OTDR port 102 provide OTDR monitoring of theinactive fiber path which is the standby fiber path 20. In FIG. 5, theOTDR interoperable trunk switch 100 has switched such that the standbyfibers 20 are now active and the OTDR signals 26, 28 provide OTDRmonitoring of the standby fibers 20. The OTDR signals 26A, 28A from theOTDR port 102 provide OTDR monitoring of the inactive fiber path whichis the primary fiber path 18 in FIG. 5.

FIG. 6 is a block diagram of an OTDR interoperable trunk switch 100Awith an OTDR port 102A which provides separate inputs for the OTDRsignals 26A, 28A thereby removing the red/blue splitter 120.Specifically, the OTDR interoperable trunk switch 100A operates in asimilar manner as the OTDR interoperable trunk switch 100 but receiveseach of the OTDR signals 26A, 28A separately and thus does not requirethe red/blue splitter 120.

OTDR Interoperable Trunk Switch—Single Wavelength (WL) andUnidirectional

FIG. 7 is a block diagram of an OTDR interoperable trunk switch 100Bwith an OTDR port 102B supporting a single wavelengthcounter-propagating OTDR signal 28A for unidirectional OTDR monitoring.Specifically, the OTDR interoperable trunk switch 100B includes thesplitter 12 in the transmit direction to split the input signal 16 onthe client-side port 106 to both line-side ports 110, 112. There is noOTDR signal in the transmit direction hence the description ofunidirectional OTDR monitoring. The receive direction includes a 2×2switch 30 with one input connected to the client-side port 108 andanother input connected to the OTDR port 102B. The outputs of the 2×2switch 30 connect to the line-side ports 114, 116. With thisconfiguration, the counter-propagating OTDR signal 28 supports OTDRmonitoring on the active fiber in the receive direction, and thecounter-propagating OTDR signal 28A supports OTDR monitoring on theinactive fiber in the receive direction.

OTDR Interoperable Trunk Switch—Single Wavelength (WL) and Bidirectional

FIG. 8 is a block diagram of an OTDR interoperable trunk switch 100Cwith an OTDR port 102B supporting a single wavelengthcounter-propagating OTDR signal 28A along with a 1×2 switch 140 forbidirectional OTDR monitoring. The OTDR interoperable trunk switch 100Cis similar to the OTDR interoperable trunk switch 100 with the 2×2optical switches 30A, 30B in FIG. 4, but the red/blue splitter 120 isreplaced with the 1×2 switch 140 which can switch an OTDR signal 142 toeither the transmit direction where the OTDR signal 142 operates as theco-propagating OTDR signal 26 or to the receive direction where the OTDRsignal 142 operates at the counter-propagating OTDR signal 28. Similarto the OTDR interoperable trunk switch 100B, the OTDR interoperabletrunk switch 100C includes the OTDR port 102B which receives the OTDRsignal 142 which is a single wavelength OTDR signal that can operate aseither the co-propagating OTDR signal 26 or the counter-propagating OTDRsignal 28 based on the 1×2 switch 140 setting.

In this manner, the OTDR interoperable trunk switch 100C cancontinuously monitor the active fiber with the OTDR signals 26, 28 andselectively monitor the inactive fiber in the receive direction or thetransmit direction one at a time. That is, the 1×2 switch 140 can sendthe OTDR signal 142 to either the receive direction or the transmitdirection of the inactive fiber path.

OTDR Interoperable Trunk Switch—Integrated OTDR Source

FIG. 9 is a block diagram of an OTDR interoperable trunk switch 100Dwith an integrated OTDR system 150. Similar to the OTDR interoperabletrunk switch 100, 100A, 100C, the OTDR interoperable trunk switch 100Dincludes the 2×2 switches 30A, 30B. However, the OTDR interoperabletrunk switch 100D does not include an OTDR port. Rather, the OTDRinteroperable trunk switch 100D includes the integrated OTDR system 150within the housing 104. The integrated OTDR system 150 provides the OTDRsignals 26, 28, 26A, 28A. The OTDR signals 26, 28 are added with theinput signal 16 and the output signal 22 via combiners 152 and the OTDRsignals 26A, 28A are connected to inputs of the 2×2 switches 30A, 30B.The OTDR interoperable trunk switch 100D can be used without an externalOTDR source (and without the OTDR ports 102, 102A, 102B).

Example Operation of the OTDR Interoperable Trunk Switch

FIGS. 10-14 are network diagrams of OTDR interoperable trunk switches100-1, 100-2 interconnected by the primary fiber path 18 and the standbyfiber path 20 illustrating a sequence of events based on a fiber cut. InFIGS. 10-14, the highlight portions indicate the signal path. FIG. 10illustrates normal operation wherein the OTDR interoperable trunkswitches 100-1, 100-2 are both set to communicate over the primary fiberpath 18. In FIG. 11, there is a fiber cut 180 on the primary fiber path18 in the eastbound direction which is detected at the OTDRinteroperable trunk switch 100-2 by a detector 24A. In FIG. 12, the OTDRinteroperable trunk switch 100-2 switches data transmission from theprimary fiber path 18 to the standby fiber path 20 which becomes theactive fiber path. A detector 24B at the OTDR interoperable trunk switch100-1 detects the loss of (data) light due to the switch by the OTDRinteroperable trunk switch 100-2. In FIG. 13, the OTDR interoperabletrunk switch 100-2 switches from the primary fiber path 18 to thestandby fiber path 20 thereby restoring bidirectional data traffic.

In FIG. 14, a highlighted path on the fiber with the fiber cut 180 showsthat the OTDR (co-propagating, counter-propagating or both) can provideinformation to help localize the fault and subsequently validate arepair.

OTDR Module

FIG. 15 is a block diagram of an OTDR module 200 interconnected to theOTDR interoperable trunk switch 100. The OTDR module 200 can connect tothe OTDR ports 102, 102A, 102B on the OTDR interoperable trunk switches100, 100A, 100B, 100C. Note, the OTDR interoperable trunk switch 100Ddoes not require an external OTDR based on the integrated OTDR system150. The OTDR module 200 can be a standalone, pluggable, or integratedinto another module in an optical networking system. For example, theOTDR module 200 can be integrated into a multiplexer/demultiplexer,optical amplifier, Optical Service Channel (OSC), or the like. Thoseskilled in the art will recognize optical networking systems can berealized with modules, network elements, nodes, line cards, etc. and thefunctionality of the OTDR module 200, the OTDR interoperable trunkswitches 100, 100A, 100B, 100C, 100D, etc. contemplate various physicalimplementations. The OTDR module 200 is presented as an example of anOTDR system in an optical networking system that can be used with theOTDR interoperable trunk switches 100, 100A, 100B, 100C.

The OTDR module 200 includes a housing 202 with client-side ports 204,206 and line-side ports 208, 210, 212. The client-side port 204 is for adata transmit direction, and the client-side port 206 is for a datareceive direction. Note, there can be other components which are omittedfor illustration purposes, such as multiple client-side ports connectedto multiplexers/demultiplexers, etc. For illustration purposes, the OTDRmodule 200 includes a single OTDR system 220 connected to a 1×2 switch222. The OTDR system 220 can monitor either the primary fiber path orthe standby fiber path (i.e., the active or the inactive fiber path)based on the setting of the 1×2 switch 222. For OTDR monitoring of theinactive fiber path, the 1×2 switch 222 is connected to the OTDR port102, i.e., the line-side port 210 is connected to the OTDR port 102. TheOTDR system 220 in this example is configured with a single output withdual wavelengths. Thus the OTDR port 102 receives a single fiber, andthe dual wavelengths are split by the red/blue splitter 120 in the OTDRinteroperable trunk switch 100.

For OTDR monitoring of the active fiber path, the 1×2 switch 222 isconnected to a splitter 224 which splits the dual wavelengths betweenthe transmit direction and the receive direction. The transmit directionincludes a combiner 226 which combines an input from the client-sideport 204 with the OTDR signal split from the splitter 224. The receivedirection includes a combiner 228 which adds the OTDR signal split fromthe splitter 224 towards the line-side port 212.

Although the present disclosure has been illustrated and describedherein with reference to preferred embodiments and specific examplesthereof, it will be readily apparent to those of ordinary skill in theart that other embodiments and examples may perform similar functionsand/or achieve like results. All such equivalent embodiments andexamples are within the spirit and scope of the present disclosure, arecontemplated thereby, and are intended to be covered by the followingclaims.

What is claimed is:
 1. An optical trunk switch system configured tosupport an Optical Time-Domain Reflectometer (OTDR) input, the opticaltrunk switch system comprising: a transmit switch having a firsttransmit input, a second transmit input, a first transmit output, and asecond transmit output, wherein the first transmit input is configuredto connect to a signal input, the second transmit input is configured toreceive a first OTDR signal input, the first transmit output isconfigured to connect to one of a primary fiber and a standby fiber, andthe second transmit output is configured to connect to the other of theprimary fiber and the secondary fiber; a receive switch having a firstreceive input, a second receive input, a first receive output, and asecond receive output, wherein the first receive input is configured toconnect to one of the primary fiber and the standby fiber, the secondreceive input is configured to connect to the other of the primary fiberand the secondary fiber, the first receive output is configured toconnect to a signal output, and the second receive output is configuredto connect to a second OTDR signal input; and one or more OTDR portsconfigured to receive the first OTDR signal input and the second OTDRsignal input.
 2. The optical trunk switch system of claim 1, wherein thefirst OTDR signal input and the second OTDR signal input are eachconfigured to monitor an inactive fiber.
 3. The optical trunk switchsystem of claim 2, wherein the signal input includes a forward travelingOTDR signal input and the signal output includes a backward travelingOTDR signal input, wherein the forward traveling OTDR signal input andthe backward traveling OTDR signal input are each configured to monitoran active fiber.
 4. The optical trunk switch system of claim 1, whereinthe first OTDR signal input and the second OTDR signal input are each ata different wavelength.
 5. The optical trunk switch system of claim 1,wherein the one or more OTDR ports include two ports, one for the firstOTDR signal input and another for the second OTDR signal input.
 6. Theoptical trunk switch system of claim 1, wherein the one or more OTDRports include one port configured to receive the first OTDR signal inputand the second OTDR signal input, and further comprising a splitterconnected to the one port and configured to split the first OTDR signalinput to the second transmit input and the second OTDR signal input tothe second receive output.
 7. The optical trunk switch system of claim6, wherein the first OTDR signal input and the second OTDR signal inputare each at a different wavelength.
 8. The optical trunk switch systemof claim 1, wherein the transmit switch and the receive switch each area 2×2 switch.
 9. The optical trunk switch system of claim 1, wherein thetransmit switch and the receive switch each are a crossbar switch. 10.The optical trunk switch system of claim 1, wherein the first OTDRsignal input and the second OTDR signal input are utilized to determineif an inactive fiber pair is operational.
 11. An optical trunk switchsystem configured to support an Optical Time-Domain Reflectometer (OTDR)input, the optical trunk switch system comprising: a transmit 2×2 switchhaving a first transmit input, a second transmit input, a first transmitoutput, and a second transmit output, wherein the first transmit inputis configured to connect to a signal input, the second transmit input isconfigured to receive a first OTDR signal input, the first transmitoutput is configured to connect to one of a primary fiber and a standbyfiber, and the second transmit output is configured to connect to theother of the primary fiber and the secondary fiber; a receive 2×2 switchhaving a first receive input, a second receive input, a first receiveoutput, and a second receive output, wherein the first receive input isconfigured to connect to one of the primary fiber and the standby fiber,the second receive input is configured to connect to the other of theprimary fiber and the secondary fiber, the first receive output isconfigured to connect to a signal output, and the second receive outputis configured to connect to a second OTDR signal input; and one or moreOTDR ports configured to receive the first OTDR signal input and thesecond OTDR signal input.
 12. The optical trunk switch system of claim11, wherein the first OTDR signal input and the second OTDR signal inputare each configured to monitor an inactive fiber.
 13. The optical trunkswitch system of claim 12, wherein the signal input includes a forwardtraveling OTDR signal input and the signal output includes a backwardtraveling OTDR signal input, wherein the forward traveling OTDR signalinput and the backward traveling OTDR signal input are each configuredto monitor an active fiber.
 14. The optical trunk switch system of claim11, wherein the first OTDR signal input and the second OTDR signal inputare each at a different wavelength.
 15. The optical trunk switch systemof claim 11, wherein the one or more OTDR ports include two ports, onefor the first OTDR signal input and another for the second OTDR signalinput.
 16. The optical trunk switch system of claim 11, wherein the oneor more OTDR ports include one port configured to receive the first OTDRsignal input and the second OTDR signal input, and further comprising asplitter connected to the one port and configured to split the firstOTDR signal input to the second transmit input and the second OTDRsignal input to the second receive output.
 17. The optical trunk switchsystem of claim 16, wherein the first OTDR signal input and the secondOTDR signal input are each at a different wavelength.
 18. The opticaltrunk switch system of claim 11, wherein the transmit switch and thereceive switch each are a 2×2 switch.
 19. The optical trunk switchsystem of claim 11, wherein the first OTDR signal input and the secondOTDR signal input are utilized to determine if an inactive fiber pair isoperational.
 20. A method comprising: providing an optical trunk switchsystem configured to support an Optical Time-Domain Reflectometer (OTDR)input, the optical trunk switch system comprising: a transmit switchhaving a first transmit input, a second transmit input, a first transmitoutput, and a second transmit output, wherein the first transmit inputis configured to connect to a signal input, the second transmit input isconfigured to receive a first OTDR signal input, the first transmitoutput is configured to connect to one of a primary fiber and a standbyfiber, and the second transmit output is configured to connect to theother of the primary fiber and the secondary fiber; a receive switchhaving a first receive input, a second receive input, a first receiveoutput, and a second receive output, wherein the first receive input isconfigured to connect to one of the primary fiber and the standby fiber,the second receive input is configured to connect to the other of theprimary fiber and the secondary fiber, the first receive output isconfigured to connect to a signal output, and the second receive outputis configured to connect to a second OTDR signal input; and one or moreOTDR ports configured to receive the first OTDR signal input and thesecond OTDR signal input.